Aircraft sustaining rotor



" AIRCRAFTSUSLMINING RoToR` V 'Fired` April 2e, 1939 M 2 `'sheesfshefat 2 um wm mm wmmmw @NNN @Y uw mvENToR A l v v I u Y AT ORN Ys Patented June 2;" 1942 UNITED ASTATUE dames Allan lJamieson' Bennett, Esher, England,

asslgnor to Autogiro Company of America, t "Philadelphia, `Pa., La corporation `of Delaware n f l `annicntion April 26, 1939, seriaiNo. 270,218

y i In GreatBritain April 28, 1938) o t `5 claim 5(01. 244-18) invention relates l rotorsk for L o gyroplanes or helicopters ofthe kind in `which the blades are capable oiat least limited leading` "j and lagging displacement` with respect to the hub;

the `bladesrnay also bejcapablefof the usualilapV ping motionl but the present'` invention is. not d primarilyV concerned with flapping. o

freely' fota-` i tive hingedwing'systemor sustaining `rotor hav-V ing freely flapping blades or wings to .malte the loY Wings either inherently resilient, or tofjoinv them" by hinges. to their common supporting member in such a `manner that the wings are permitted a* restricted displacementrelatively to one another in the plane ofcrotation withyieldable connec-oi tions betweenthewings tendingduring rotation l to maintain, than in symmtncn mation.` d l,

It has `however hitherto beenthe .Iusual prac-` tice `at least in gyroplanes to" connect the *rotor` blades to their supporting members L `ilisually con` sisting of drag links" articulatedfto the hubfor flapping) by meansof pivotsallowing the blades" to swing freely in the leading and lagging direc-g` V tion relative to .the hubland toldam-p the moven ments-cf the blades relative` to the hub, about the drag pivotsby means of frictional dampers. s

It has been found (thatthe frictional restraint stiffness for this purpose.

The `present invention therefore in essence consists in the provision, in combination, of a pivotal articulation idrag pivot) permitting un"-V "restricted leading andlagging o fthe blade, but strongly'lresistant to twisting infariy plane con` l taining its axis,` and aresilient connection re-" sistant to leading and lagging displacement of the blade. Although the resilient connection o of the present invention contemplates preferably the `elimination of the ordinary friction damper for 4the drag pivot, the measure of resiliency'of the connection may .convenientlybe defined'in `terms `offcornparison with the well-known fric'- tion d damper installation.` `Thus,'the resilience of the connection is prefer-ably so selected or adjusted that the maximum restoring moment* exercised thereby ontheblade about'` the drag pivot axisin the course of the leading and lagging oscillation in normal flight is substantially equivalent to the `moment which would be reduired to overcome the limiting frictionalresistance of a f rictional damper of the usual kind when appropriately adjusted, and with the resilient connection so designed or t'tdjusted;A the natural freailorded by dampers `may conveniently be replaced bya. resilient restraint if properly con` structed andgarranged `in accordance Vlwith the presentinvention.` l

It is now `known that intermedie-connections v tending to maintain `syrnmetrylin'the planeof rotation are not only unnecessary but maybe disadvantagteous. It would `therefjonf: appear that the requisite restraint on leading and lagging quency of theleading-lagging oscillation is such that; resonance with the forced vibrationsdoes not occur.

The resilient connection may,` if desired;l be so ,disposed and anchored, and of sufficient strength and stiffness in tension, that it can transmit 'theA centrifug'alforce of the blade toV the huband l thereby relieve the jdrag 1oading`.ll o o Y n A Means are preferably provided for adjusting displacements of the blades could be obtained by suppressing the drag" pivots altogether andby making the root member of the4 blades suiii" ciently flexible initheleadin'g and lagging plane to provide` fora leading land lagging" displace` ment offthe blade relatively to the hub` placed-"under the `required amount of resilient` restraint.` ,v y "-The constructionlof a flexible `blade `root of this `kind having the appropriate resilience` to impose thel'required amount ofrestraint on the.` leading and laggingloscillation'of the blade, and o to give said oscillation such a natural frequency thatthere would be no danger of resonancewith the forced vibrationsencountered inl night, and havingat the 'sameftime adequatejstrength to resist the centrifugalloading during rotation, would not present any serious difficulty, but such provided in the specific `example hereinafter the resilience ofthe connection restraining displacement about the drag pivot without dismantling Vthewhole assembly of the blade root, and

a convenient form of device for this purpose is described with" reference to the accompanying drawings. d t it It is `to be understoodthatthe references to drag pivots are not to be read as limited tol pure drag pivots, i. e.; pivots on which the blade moveo ment is pure1yonef`1ead and lag; butts memeinclined either'in the plane containing the axis' ingLany pivot or complex pivotal articulation about whichA the blade" movement is principally one of 4lead and lag; thus the drag pivot may be ofrotation of the'huband the axis of the blade so` that the leading and laggingfdisplaceme'nt is t t accompanied `byvariation of pitch angle, or may a flexible 1 root structure 'would haveinadequate 55 be inclined inaplane perpendicular to the axis` l in torsion junless otherwise reinforced l pivot of centrifugal of the blade, so that leading and lagging movement is accompanied by flapping (which may be compensated by displacement about the usual napping pivot). It must be understood however that if the blade articulation includes a flapping pivot as well as a drag pivot (as above broadly defined), and if it be desired to retain fully freedom of movement about the flapping pivot, the Vresilient means restraining movement about the drag pivot must be so disposed and connected that movement upon the flapping pivot is in no way restrained. This will be the case if a drag link is connected to the hub by means of a flapping pivot and to the blade by" means of a drag pivot and the resilient connection is effective l5 between the drag link and the blade. Alternatively the blade may be connected by means of a flapping pivot to a link or trunnion block which is connected to the hub by means ,of a drag pivot and the resilient connection may be mounted so 2o as to be effective between the hub and the link 4ortrunnion block.

The combination of a drag pivot and a resilient restraint as herein described affords a blade attachment giving lthe required restraint of leadg5 ing and `lagging displacement and having adequate torsional stiffness vand strength to resist centrifugal force. A

The accompanying drawings illustrate by way of example a preferred constructional embcdiment of this invention as applied to a blade root assembly for the rotor of a gyroplane or helicopter in whicha drag link is connected to the rotor hub by means of a flapping pivot and the rotor blade isV connected to the drag linkj by combined pivotal and resilient connections as hereinbefore set forth.

Ihe following description has reference to the accompanying drawings, in which: Y

Fig. 1 is a view inside elevation of a gyroplaneAO embodying the present invention;

Fig. 2 is a .view in side elevation partlyl in sec-r Vtion showing the connections of one of the rotor blades to the rotor hub; Y Fig. 3 is a plan view of the same. 4r

The gyroplane'of Fig. 1 comprises the usual bodyIIl, engine II, airscrew I2 and undercarriage I3. Apyramidal pylon structure I4 of the usual kind supports a rotor head assembly I5 in whichthe rotor hub I6 is rotatably mounted 50 in bearings (not shown). The rotor head assembly |5 also includes rotor driving gear of the usual kind, the drive being taken from a transmission shaft I1 which is connected to the Ver1- gine r-I I- in the known manner through gearing and a clutch, these parts being contained within the body IU and not shown on the drawings.

In the example shown, a three-bladed rotor is provided, two of the blades 26 being shown -in Fig. 1.

Referring more particularly to Figs. 2 and 3,

the rotor hub I6 terminates upwardly in a forked structure carrying flapping pivot pins I8 of which one is shown in Figs. 2 and 3. A drag link I9 articulates for napping on the flapping pivot 65 pin II! and its outer-end is bored at right angles to the axis of the flapping pivot to receive a bushy 20 in which a drag pivot pin 2| is rotatable. The ends of the' latter are secured in the upper and lower members 22, 2,3 of aforked structure constituting the inner end of a blade rootsocket V24 in which is secured the root end of ablade spar 25 carrying the rotor blade 26. The drag pivot assembly is completed by cover plates 21 secured p by a central through-bolt 28. The upper member 22 of the fork end of the blade socket 24 is provided with a slot 29 in which engages a pin 30 secured in the drag link I9 to limit movement upon the drag pivot; the pin 30 is made easily removable to permit folding of the rotor blades. The root end of the blade spar 25 is further connected to the drag link I9 by means of a resilient connection consisting of a straight metal tube 3| whose inner end is anchored by means of a through-bolt 41 in the larger half 3|' of a split vclamp 3|', 32 which is secured on the shank of the drag link by means of clamping bolts 46. The outerend of the tube 3| is provided with an adjustable collar 33. To locate the collar 33 on the tube 3| the inner surface of the collar 33 is suitably shaped to engage one or other of a series of notches 34 formed in the outer surface of the tube 3| and the collar is further secured by means of a set screw 36 engaging inbne or other of a series of tapped holes `35 in the tube 3|. This arrangement 'provides a convenient means by which the position ofthe collar 33 along the length of the tube 3| may be adjusted. The outer surface of the collar 33 is machined to a' spherical form and engages between two vertical plates 31 secured by means of bolts 3B to a pair of transmission flanges 39 welded-or otherwise secured to one, half 4| of a split clamp 4|, 42 which is clamped about the root end of the blade spar 25 by means of bolts 43. The plates 31 are further rigidly secured in correct parallel spacing by means of a cover plate 44 attached to the plates 31 by means of studs 45. Y Since the resilience, i, e., the restoring force for a given deflection, of the tubular connection 3| dependson the length between its abutments it will be seen that by adjustment `along the length of thetube 3| of the collar 33 which abuts against the plates 31, the effective length of the spring constituted by the tube 3| can be easily regulated. It will also be seen that the spherical external shape of the collar 33 effectively`prevents binding between the plates 31 so that the tube 3| acts in the same` manner as a leaf spring encastre at one end and free at the other. It will of course be recognised that if thetube 3| were effectively encastre at its outer end'as well as at its inner end its effective stiffness would be approximately quadrupled. VThe location of` the collar 33 between the plates 31 further allows of some longitudinal sliding when the rotor blade i 26 leads or lags about the drag pivot 20, 2| andi it will be seen that if such sliding were not provided for the tube 3| would be stressed not only l as aprbeam but alternately as a strut or tension member and additional stresses would be thrown 'on the clamping assembly 42, 43, etc., and thereby on the blade spar 25. It has already been explained that the maxl- 0 mum restoring moment on the tube 3| in normal flying conditions should be approximately equalQ to the' moment required to overcome the static friction of a friction damper as usually applied to a drag pivot when correctly adjusted for the rotor in question and the length and stiffness of the. tube 3|V are therefore lselected accordingly; finaladjustment of the effective resilience of the connection constituted by the tube 3| is effected by adjusting the'position of the collar 33.

In the arrangement illustrated in the drawings and described above the centrifugal force of the blade is entirely transmitted by the drag pivot 20, 2| since the'nature of the joint between the collar 33 and the plate 31 effectively relieves the tube 3| of tensile loading. Il?,A however,.it is desired to utilise the tensile strength of the tube 3l for relieving the drag pivot 2li, 2| of centrifu? gal-loading a differentV form of anchorage at theI outer end of the tube 3I will benecessary and it will be recognised that if the tube 31 is'anehored at both ends in such a manner as to be capable of sustaining tensile loads it will necessarily be encastre at both ends and the consequentialincrease of its effective `stiffness will have to bel Y taken into account.` However, if both ends of the tube 3l are encastre some end play in the conthe drag pivot from being subjected to severe alternate loading.

It must be understood that there 'isnothing in the detail of construction ofthe blade root structure and connections illustrated in Figs.`2` and 3 which is necessarily peculiar to the embodiment in a gyroplane as shown in Fig. 1 which is given merely by way of example.` The structure and connections shown in Figs. 2 and 3 can be applied equally to a helicopter.

What I claim is: f l 1. In an aircraft sustaining rotor comprising a hub and a blade, mechanism `connecting the blade to the `hub including a pivotal articulation Whose axis intersects thegeneral plane of rotation in *a position to accommodate leading and lagging movement of the blade relative to the hub and which is vresistant to twisting in planes containing its axis, and a resilient device resistant to displacement of the blade about said pivotal articulation, said device comprising an elongated resilient memberfhaving its ends operatively associated respectively with anelement of the blade and an element of said connecting mechanism, one of said ends being fixedly secured to its associated element and the other end o tion is adjustable to'be` out of phase with the. nor- 'mal rotational frequencyfof the rotor.

whose axis intersects the` general plane of rotation in a position to accommodate leading and lagging movement of the blade relative to the hub and which is resistant to twisting in planes containing its axis, and a resilient device resist-V tively with an'element of the blade and an ele- `ment; of said mounting mechanism, one end being'. xedly Vsecured to the latter element at a point inboard of the pivot, and the other end hav- "ing means for contacting the blade which is adjustable to different positions lengthwise of saidmember' to `alter-the position of application o forces whereby the naturalirequency of oscilla- In an aircraft `rotorhaving" a hub andan i airfoil blade rotatable about the hub axis,y blade mounting mechanism comprising a flight pivot providingl fordisplacement movements of the blade in a sense involving .swinging of the longitudinal blade axis to both sides of a predetermind normal,V an elongated resilient member.

associated with an element of the blade and with an elementof the mounting in position to be subjected only "to lateral deflection by blade move- 30 end of said member to one of said elements, and

ing cooperation may be varied to change the natural frequencyof said member.

2. In an aircraft sustaining rotor comprising a hub and a blade, mechanism mounting the blade on the hub including a'pivotal articulation the'other .abutment meansrhas relative longitudinal sliding engagement with the other element upon blade displacement at each side of the predetermined normal. 7

5. A construction according to claim 3 wherein one of said abutment means has a device for adjusting it to various xed positions along the v length of said member to alter the xed effective length thereof.

JAMES ALLANvJAMIESON BENNETT. 

